Severe shortages of human donor organs and cells for transplantation have resulted in great interest in the use of pigs as organ donors. Associated with the clear benefits of xenotransplantation is the risk of infection of the recipient with porcine microorganisms introduced along with the donor organ. Of primary concern are those organisms that can be transferred in a latent state in the xenograft recipient. Retroviruses fall into this category. Endogenous retroviruses form a normal part of the genomic DNA of all pig cells and thus can not be removed by techniques such as barrier derivation that clears other microorganisms. As such, porcine endogenous retroviruses (PERV) represent a particularly problematic safety concern for xenotransplantation. All breeds of pig tested to date produce PERV capable of infecting human cells. BioTransplant has identified a particular haplotype of animals within its inbred miniature swine herd that does not produce PERV capable of infecting human cells. Consequently these animals might represent a source of safer organs for xenotransplantation. Characterization of these animals is proposed in this Phase I application. PROPOSED COMMERCIAL APPLICATIONS: The critical worldwide shortage of donor organs and ever-increasing waiting lists for organ recipients have long been recognized. Xenotransplantation is a long-term solution to this chronic shortage. A roadblock to the acceptance of this strategy has been concern about the risk for transmission of pathogens from the donor to the host. BioTransplant has developed a herd of miniature swine that do not produce porcine endogenous retrovirus capable of infecting human cells. This quality provides a significant commercial advantage for their use as the herd of choice for xenotransplantation